The present invention relates to an apparatus for separation of at least one component from a fluid sample, and then analysis of the at least one component. More particularly, the present invention relates to an apparatus and method for separating and analyzing the quantities of organics, such as volatile organic compounds (VOCs) in a fluid sample such as ground water, drinking water or waste water.
In recent years, there has been an increased awareness of the potential contamination of water with organics, which include, but are not limited to nonvolatile organic compounds, alcohols and polymers, and volatile organic compounds (VOCs) such as benzene, toluene, xylene, perchloroethylene, and trichloroethylene. Many of these contaminants in groundwater supplies have originated from the excessive and widespread use of chlorinated hydrocarbons as degreasers, leaks from underground storage tanks, leachate from municipal and industrial landfill sites, or releases in industrial effluent streams.
Methods to separate these contaminants have been developed. One such method, the purge and trap method, is a dynamic head space procedure carried out by purging the VOCs from the fluid sample with the help of an inert fluid, such as N2. The purged VOCs are then trapped in a material to which the VOCs reversibly adsorb. After a predetermined period of time, the VOCs are released from the trap in a concentrated form, and injected into a detector, such as a gas chromatograph or a gas chromatograph coupled to a mass spectrometer. However, this method possesses inherent limitations. In particular, cryogenic trapping of the organic contaminant is required prior to analytical analysis of the contaminate. Cryogenic trapping can result in freezing of moisture in the trap, and a decrease of the efficiency of the apparatus. Furthermore, cold spots in the plumbing of the apparatus also results in carryover problems and memory effects. Consequently, blanks must be run between fluid samples.
Another method used is liquid-liquid extraction. In this method, an organic solvent in which the organic is very soluble, is mixed with the fluid having the VOC contaminant. During this mixing, the organic becomes solubilized in the organic solvent, and thus is removed from the fluid. However, this method also contains inherent limitations. Initially, it involves the use organic solvent. Such solvents are themselves hazardous waste, which are very expensive to dispose of after use. Another potential problem with this method involves replacement costs for replacing solvent containing solubilized organics, which is discarded.
Membrane extraction has also been used to remove and measure a contaminant from a fluid sample. In this method, a fluid sample containing an organic is continuously contacted with a membrane having chemical and physical properties that permits the organic to diffuse into and across the membrane, but prevents the fluid sample from diffusing across and into the membrane. As a result, the organic is separated from the fluid. Hence, this method does not require any solvents or solid phases. However, this method as generally used heretofore, possesses inherent limitations. Initially, such methods are generally used in continuous monitoring, and require large amounts of fluid sample. Hence, it is very difficult with presently known membrane extraction systems to remove the organic from a small amount of fluid sample. Furthermore, in order to obtain accurate measurements of the organics in the fluid, an equilibrium must be established in the membrane such that the amount of organic leaving the membrane and the amount entering the membrane are in a steady state. Until this steady state is achieved, measurements of the amount of organic in the fluid will be inaccurate. Moreover, in order to reach this steady state, the fluid sample must flow continuously through the feed chamber, which requires large amounts of fluid sample.
Still another drawback to this method is the lag time involved in obtaining accurate measurements. This lag time is the result of the need to equilibrate the membrane to the concentration of organics in the solution, as explained above, and the necessity of the organics to diffuse through a boundary layer of fluid formed on the surface of the membrane prior to diffusing through the membrane itself.
Accordingly, what is needed is an apparatus and method that permit separation and analysis of organics in a discreet sample of fluid, such as water, having a small volume, e.g., about 1 xcexcl to about 1 ml, or a moderate volume, e.g. about 1 ml to about 10 ml.
What is also needed is an apparatus or method of separating and analyzing organics in a discreet fluid sample that is not dependent upon equilibration of a membrane, i.e., the reaching of a steady state of component traversing the membrane. As a result, samples of fluid with vastly different concentrations of organics can be analyzed quickly and accurately.
The citation of any reference herein should not be construed as an admission that such reference is available as xe2x80x9cPrior Artxe2x80x9d to the instant application.
There are provided, in accordance with the invention, a new and useful apparatus and method for separating and analyzing at least one component of a fluid sample that do not possess the shortcomings of apparatuses and methods described above. Hence, the present invention is not dependent upon equilibration of the permeation of the component through a membrane, and can analyze a fluid sample having a discreet volume, even if the volume is small (about 1 xcexcl to about 1 ml) or medium (about 1 ml to about 10 ml) in size. As a result, the present invention offers the advantages of permitting analysis of discreet volumes of fluid samples accurately and quickly.
Broadly, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample, the apparatus comprising a feed chamber having an entrance and an exit, a first flow means for flowing a first carrier fluid through the feed chamber, a means for injecting a pulse of fluid sample into the flow of the first carrier fluid such that the pulse of fluid sample enters the feed chamber, an exit chamber downstream from the feed chamber, at least one membrane through which the at least one component can selectively permeate, wherein the at least one membrane is located between the feed chamber and the exit chamber, and is fluid registry with the feed chamber and the exit second chamber, a detector in fluid communication with the exit chamber, wherein the detector analyzes the at least component that passes through the membrane and enters the exit chamber, and a second flow means for flowing the at least one component which passes through the at least one membrane and enters the exit chamber, to the detector.
Furthermore, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample as described above, wherein the fluid sample comprises an aqueous solution, the at least one component comprises an organic, and the first carrier comprises a water, water with salt or other additives, organic solvents, nitrogen, carbon dioxide, argon, neon, or a combination thereof.
Numerous means are presently available to the skilled artisan to form the first flow means of the invention. A particular means having applications herein comprises a first reservoir which holds the first carrier fluid upstream from the feed chamber, and a pump connected to the first reservoir and in fluid communication therewith. The pump pumps the first carrier fluid from the first reservoir, through the entrance, and then through the exit of the feed chamber. Thus, a flow of the first carrier fluid through the feed chamber is created. Other means of forming such a flow include placing the first carrier fluid in the first reservoir under pressure, and locating a valve downstream from the first reservoir and upstream of the entrance of the feed chamber, wherein the valve is in fluid communication with the first reservoir and the feed chamber. When the valve is opened, the pressure forces the first carrier fluid from the first reservoir and through the feed chamber. Still another means comprises locating a drawing means, such as a vacuum pump in fluid communication with the exit of the feed chamber. When the vacuum is activated, it will draw the first carrier fluid from the first reservoir, and through the feed chamber.
In addition, the present invention extends to the apparatus for separating and analyzing at least one component of a fluid sample as described above, wherein the means for injecting the pulse of fluid sample into the feed chamber comprises a multi-port valve upstream from the feed chamber and downstream from the first reservoir, wherein the multi-port valve is in fluid communication with the first reservoir and the feed chamber, and comprises a first port through which the pulse of fluid sample is injected into the flow of the first carrier fluid. Optionally, a sample loop can be fixed to the multi-port valve. This loop allows one to vary the volume of the pulse of fluid sample injected into the apparatus. Furthermore, such an injection can be made with a syringe in fluid communication with the multi-port valve, or via a reservoir holding the fluid sample, which is in fluid communication with the multi-port valve.
Optionally, the apparatus of the invention can further comprise an a means for flowing a substantially inert purge fluid into the feed chamber after the pulse of fluid sample has passed through the feed chamber. This purge fluid disrupts the fluid layer which develops over the membrane in the fluid chamber, and thus decreases the response time of the instrument. Furthermore, the purge fluid purges any component of the fluid sample that is within the membrane but has not completely passed through the membrane. Hence, these components are purged from the membrane and enter the exit chamber, thus increasing the accuracy of the separation and analysis of the apparatus. Numerous means of flowing the purge fluid into the feed chamber are readily available to one of ordinary skill in the art. A particular means comprises a switching valve located upstream from-the multi-port valve and downstream from the first reservoir, and in fluid communication with the first reservoir and the multi-port valve, and a second reservoir for holding the substantially inert purge fluid in fluid communication with the switching valve. The switching valve can be readily manipulated to prevent the first carrier fluid from flowing into the feed chamber after the fluid sample has passed through the feed chamber, and to permit the purge fluid to enter the feed chamber. Also, numerous fluids can serve as the purge fluid. In a particular embodiment, wherein the fluid sample comprises an aqueous solution and the at least one component comprises an organic, the substantially inert purge fluid comprises N2, CO2, neon or helium.
Furthermore, as explained infra, the at least one membrane can be symmetrical or asymmetrical in structure, depending upon the application. In a particular embodiment, the at least one membrane comprises at least one hollow fiber having a bore and an outer surface, and the at least one hollow fiber is contained within a shell, such that the bore defines the feed chamber, and the shell and the outer surface of the hollow fiber define the exit chamber. Furthermore, in a preferred embodiment, the bore of the at least one hollow fiber membrane has a diameter of about 0.305, and the at least one hollow fiber has an outer diameter of 0.635 mm.
Furthermore, the at least one fiber of the invention can be comprised of nonporous hydrophobic material, such as polydimethylsiloxane (silicone rubber), nitrile rubber, neoprene rubber, silicone-polycarbonate copolymers, fluoroelastomers, polyurethane, polyvinylchloride, polybutadiene, polyolefin elastomers, polyesters, or polyethers, to name only a few. In a particular embodiment, the at least one membrane is comprised of polydimethylsiloxane.
In addition, the at least one membrane of the apparatus can be a membrane composite, comprising a porous membrane having a first and second surface, and a nonporous hydrophobic membrane permanently disposed on the second surface of the porous membrane, such that the first surface of the porous membrane is in fluid registry with the exit chamber, and the nonporous hydrophobic membrane is in fluid registry with the feed chamber. Any of the materials described above for use in the at least one membrane of the invention have applications in the nonporous hydrophobic membrane of the membrane composite. Further, examples of materials which can be used in the porous membrane include, but are not limited to, polypropylene, polyethylene, polytrimethylpentene, polytetrafluoroethylene, polyvinylidene difluoride, or polysulfone, and can have pores ranging in size from about 6 to about 500 xc3x85.
Furthermore, in an embodiment of the invention, a membrane module is used which comprises a plurality of membranes housed within the shell. Hence, the surface area of the at least one membrane can be increased, which increases the efficiency of the present invention.
In addition, an apparatus for separating and analyzing at least one component of a fluid sample of the invention can further comprise an injection means for injecting the at least one component which passes through the membrane and enters the exit chamber, into the detector, wherein the injection means is located downstream from the exit chamber, and upstream from the detector, and in fluid communication with the exit chamber and the detector. An example of an injecting means having applications herein comprises a multi-port valve. Another injection means having applications herein comprises a trap means comprising a column having a first end in fluid communication with the exit chamber and a second end in fluid communication with the detector, wherein the column is packed with a packing material to which the at least one component can reversibly adsorb, and a releasing means which desorbs the at least one component from the packing material. As a result, the at least one component which passes through the membrane and enters the exit chamber, is flowed via a second flow means, which is described infra, from the exit chamber to the trap means. When released from the trap means, the at least one component then flows to the detector via the second carrier fluid.
Numerous materials, such as xe2x80x9cTEFLONxe2x80x9d, polypropylene, stainless steel or glass, can be used to form the column of the trap means. Furthermore, numerous packing materials can be used in the column. In a particular example, wherein the at least one component is an organic, the packing material comprises xe2x80x9cTANEXxe2x80x9d, silica gel, or a carbon based sorbent like charcoal, xe2x80x9cCARBOTRAP Cxe2x80x9d (Supelco, Inc., Supelco, Pa.), xe2x80x9cCARBOSIEVExe2x80x9d, or a combination thereof. In a particular embodiment of the invention, wherein the at least one component is an organic, the column comprises a length of 15 cm, an outer diameter of 0.53 mm, is comprised of stainless steel, and is packed with xe2x80x9cCARBOTRAP Cxe2x80x9d.
Moreover, in this embodiment, the releasing means comprises a means for heating the packing material such that the organics can desorb from the packing material, and then flow into the detector via the second carrier fluid, described infra. A particular heating means having applications with a stainless steel column, comprises a power supply electrically connected to the column, such that an electric current is applied to the column, and the column undergoes resistive heating. As a result of this resistive heating, the packing material is heated and the at least one component can desorb from the packing material, and flow into the detector via the second carrier fluid.
The present invention further extends to an apparatus for separating and analyzing at least one component of a fluid sample, as described above, wherein the detector comprises a high performance liquid chromatograph, a gas chromatograph coupled to a mass spectrometer, a capillary electrophoresis instrument, a mass spectrometer, a total organic carbon analyzer, or an infra red (IR), ultraviolet (UV), Raman or fluorescence spectrometer, to name only a few.
Furthermore, as mentioned above, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample, further comprising a second flow means for flowing the at least one component which passes through the at least one membrane, from the exit chamber, optionally to the injection, and then to the detector. In a particular embodiment of the invention, the second flow means comprises a third reservoir holding the second carrier fluid, wherein the second reservoir is in fluid communication with the exit chamber, such that the second carrier fluid flows from the second reservoir through the exit chamber, optionally to the injection means, and then to the detector. Examples of the second carrier fluid having applications herein include, but certainly are not limited to, nitrogen, hydrogen or helium.
Furthermore, the present invention extends to a process for separating and analyzing at least one component of a fluid sample, practiced with an apparatus comprising a feed chamber having an entrance and an exit, a first flow means for flowing a first carrier fluid through the feed chamber, means for injecting a pulse of fluid sample into the flow first carrier fluid such that the pulse of fluid sample enters the feed chamber, an exit chamber downstream from the feed chamber, at least one membrane through which the at least one component can selectively permeate there through, wherein the at least one membrane is located between the feed chamber and the exit chamber, and is fluid registry with the feed chamber and the exit second chamber, a detector in fluid communication with the exit chamber, wherein the detector analyzes the at least component that passes through the membrane and enters the exit chamber, and a second flow means for flowing the at least one component which passes through the at least one membrane and enters the exit chamber, to the detector. The process comprises the steps of flowing the first carrier fluid through the feed chamber, injecting the pulse of fluid sample into the first carrier so that the pulse of fluid sample enters the feed chamber, and detecting the at least one component which passes through the at least one membrane and enters the exit chamber.
Naturally, the at least one membrane of the process can be symmetrical of asymmetrical in structure. In a particular embodiment, the at least one membrane comprises at least one hollow fiber having a bore and an outer surface, and the at least one fiber is contained within a shell, such that the bore defines the feed chamber, and the shell and the outer surface of the at least one hollow fiber define the exit chamber. The hollow fiber membrane of the invention can have numerous dimensions, depending upon the application. In a particular embodiment the at least one hollow fiber has an inner, or bore diameter of 0.305 mm and an outer diameter of 0.635 mm.
Furthermore, in a particular embodiment of the process, the at least one membrane is comprised of a nonporous hydrophobic material. Numerous nonporous hydrophobic materials such as polydimethylsiloxane (silicone rubber), nitrile rubber, neoprene rubber, silicone-polycarbonate copolymers, fluoroelastomers, polyurethane, polyvinylchloride, polybutadiene, polyolefin elastomers, polyesters, or polyethers, to name only a few, have applications in the invention. In a preferred embodiment of the invention, the at least one membrane is comprised of polydimethylsiloxane (silicone rubber).
Further, the at least one membrane can also be a membrane composite, comprising a porous membrane having a first and second surface, and a nonporous hydrophobic membrane permanently disposed on the second surface of the porous membrane, such that the first surface of the porous membrane is in fluid registry with the feed chamber, and the nonporous hydrophobic membrane is in fluid registry with the exit chamber. Numerous porous materials can be used in the porous membrane of the membrane composite. Particular examples of such materials include polypropylene, polyethylene, polytrimethylpentene, polytetrafluoroethylene, polyvinylidene difluoride, or polysulfone, to name only a few. Also, the pores of the porous membrane can vary in size, from about 6 to about 500 xc3x85, depending upon the particular application. One of ordinary skill in the art is readily able to determine the particular size pores needed for a particular application. Furthermore, the nonporous hydrophobic membrane can be comprises of any of the nonporous hydrophobic materials discussed above. In a preferred embodiment of the membrane composite, the porous membrane comprises polypropylene, and the nonporous hydrophobic membrane comprises polydimethylsiloxane (silicone).
The present invention further extends to a process for separating and analyzing at least one component of a fluid sample as described above, wherein the step of flowing the first carrier fluid through the feed chamber comprises providing a first reservoir which holds the first carrier fluid upstream from the feed chamber, and providing a pump in fluid communication with the first reservoir, such that the first carrier fluid is pumped through the feed chamber. Various fluids have applications as the first carrier fluid the invention. Particular examples include water, water with salt or other additives, organic solvents, nitrogen, carbon dioxide, argon, neon, or a combination thereof.
In addition, the present invention extends to a process for separating and analyzing at least one component of a fluid sample, wherein the step of injecting the pulse of fluid sample into the feed chamber comprises a multi-port valve upstream from the feed chamber and downstream from the first reservoir. The multi-port valve is in fluid communication with the first reservoir and the feed chamber, and comprises a first port through which the pulse of fluid sample is injected into the flow of the first carrier fluid. Hence, as the first carrier fluid flows from the first reservoir into the feed chamber, the pulse of fluid sample is carried into the feed chamber, where the at least one component is separated from the fluid sample.
Furthermore, the present invention extends to a process for separating and analyzing at least one component of a fluid sample, comprising the steps of flowing the first carrier fluid through the feed chamber, injecting the pulse of fluid sample into the first carrier so that the pulse of fluid sample enters the feed chamber, flowing a substantially inert purge fluid into the feed chamber after the pulse of fluid sample has passed through the feed chamber, and detecting the at least one component which passes through the at least one membrane and enters the exit chamber. In a particular embodiment of the invention, the step of flowing the substantially inert purge fluid into the feed chamber comprises providing a switching valve upstream from the multi-port valve and downstream from the first reservoir, and in fluid communication with the first reservoir and the multi-port valve, and providing a second reservoir for holding the substantially inert purge fluid in fluid communication with the switching valve. This step of the process also comprises operating the switching valve such that the first carrier fluid is prevented from entering the feed chamber after the pulse of fluid sample has passed through the feed chamber, and the substantially inert purge fluid is permitted to flow from the second reservoir into the feed chamber after the pulse of fluid sample has passed through the feed chamber. When in the feed chamber, the purge fluid disrupts the boundary layer which forms on the surface of the at least one membrane, and purges any component in the membrane. Hence, the components in the at least one membrane pass through and enter the exit chamber, resulting in increased accuracy and decreased lag time for the present invention. Numerous fluids can be used as a substantially inert purge fluid. In a particular embodiment, wherein the fluid sample comprises an aqueous solution, and the at least one component comprises an organic, the purge fluid comprises N2, CO2, neon or helium.
Furthermore, the present invention extends to a process for flowing a substantially inert purge fluid into the feed chamber as described above, further comprising the step of injecting the at least one component which passes through the membrane and enters the exit chamber, into the detector. In a particular embodiment, wherein the at least one component comprises an organic, the injecting step comprises the steps of providing a trap means comprising a column having a first end in fluid communication with the exit chamber, and a second end in fluid communication with the detector, wherein the column is packed with a packing material to which the organics can reversibly adsorb. The injection step also comprises providing a releasing means for releasing the at least one component trapped in the trap means, so that the second carrier can flow the released at least one component into the detector. The column of the trap means can be made of any material that does not chemically react with the packing material, the at least one component, and the second carrier fluid. Examples of such materials include, but are not limited to, stainless steel, xe2x80x9cTEFLONxe2x80x9d, polypropylene, or glass. Furthermore, when the at least one component comprises an organic, the packing material is comprised of xe2x80x9cTANEXxe2x80x9d, silica gel or a carbon based sorbent such as charcoal, xe2x80x9cCARBOTRAP Cxe2x80x9d (Supelco, Inc., Supelco, Pa.), xe2x80x9cCARBOSIEVExe2x80x9d, or a combination thereof. In a particular embodiment the column of the trap means comprises a length of about 15 cm, an outer diameter of about 0.53 mm, is comprised of stainless steel, and is packed with xe2x80x9cCARBOTRAP Cxe2x80x9d.
Furthermore, numerous releasing means, i.e., means for heating the packing material such that the organic desorbs from the packing material, have applications herein and are readily available to the skilled artisan. One such heating means comprises a flame place under the column, such that the flame heats the column, which in turn heats the packing material. Another means for heating the column comprises bombarding the column with electromagnetic radiation, such as a microwave, or a laser, which the column can absorb. Such absorption will heat the column and in turn, heat the packing material. Still another means of heating the packing material, wherein the column is made of a material that conducts an electric current, involves conducting an electric current through the column. Hence, in this embodiment of the invention, the releasing means comprises a power supply electrically connected to the column, such that an electric current is applied to the column, and the column undergoes resistive heating which, in turn, heats the packing material.
Naturally the detectors having applications in an apparatus of the invention, such as a gas chromatograph, a high performance liquid chromatograph, a gas chromatograph coupled to a mass spectrometer, a capillary electrophoresis instrument, a mass spectrometer, a total organic carbon analyzer, or an infra red (IR), ultraviolet (UV), Raman or fluorescence spectrometer.
Also, the present invention extends to a process for separating and analyzing at least one component of a sample fluid as described above wherein the step of detecting the at least one component which passes through the at least one membrane comprises flowing a second carrier fluid through the exit chamber, and to the detector. The second carrier fluid carries the at least one component from the exit chamber to the detector for analysis. The step of flowing the second carrier through the exit chamber comprises providing a third reservoir which hold the second carrier fluid under pressure. The third reservoir is in fluid communication with a valve, which is in fluid communication with the exit chamber, so that the valve is downstream of the third reservoir and upstream of the exit chamber. When the valve is opened, the pressure of the second carrier fluid in the third reservoir causes the second carrier fluid to flow from the third reservoir, through the exit chamber, through an injection means, if present, and ultimately to the detector. Numerous fluids can be used as the second carrier fluid in the process of the invention. Particular examples include nitrogen, hydrogen or helium.
In another embodiment, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample, wherein the apparatus comprises a feed chamber having an entrance and exit, a first flow means for flowing a first carrier fluid through the feed chamber, means for injecting a pulse of fluid sample into the flow of the first carrier fluid such that the pulse of fluid sample enters the feed chamber, and an exit chamber downstream from the feed chamber. This embodiment also comprises at least one membrane through which the at least one component can selectively permeate, wherein the at least one membrane is located between the feed chamber and the exit chamber, and is fluid registry with the feed chamber and the exit chamber. Furthermore, this embodiment of the apparatus of the invention comprises a means for flowing a substantially inert purge fluid into the feed chamber after the pulse of fluid sample has passed through the feed chamber, a trap means located downstream from the exit chamber and in fluid communication therewith, wherein the at least one component that permeates through the at least one membrane can be trapped. In addition, this embodiment of the invention comprises a releasing means connected to the trap means, wherein the releasing means releases the at least one component trapped in the trap means. This embodiment of apparatus of the invention also comprises a detector in fluid communication with the trap means, wherein the detector analyzes the at least component released from the trap means, and a second flow means for creating a flow of the at least one component from the exit chamber to the trap means, and then from the trap means to the detector when the at least one component is released from the trap means by the releasing means. In a particular embodiment, the pulse of fluid sample has a discreet volume ranging from 1 xcexcl to, and including 10 ml.
Furthermore, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample as described above, wherein the first flow means comprises a first reservoir for holding the first carrier fluid, which is upstream from the feed chamber, and is in fluid communication therewith. Furthermore, a pump, such as peristaltic pump, is in fluid communication with the first reservoir and the feed chamber. Hence, the first fluid carrier is pumped from the first reservoir and into and through the feed chamber. Examples of pumps having applications herein include a peristaltic pump, a mechanical pump or a gear pump, to name only a few. Other means of creating the first flow include placing the first carrier fluid in the reservoir under a pressure and providing a valve located downstream from the first reservoir and upstream from the feed chamber. When the valve is opened, the pressure of the first carrier in the first reservoir will cause the first carrier to exit the first reservoir and flow to the feed chamber. Another means for creating such a flow is to provide a vacuum means, such as with a vacuum pump in fluid communication with the exit of the feed chamber. When, the vacuum means is operating, it will draw the first carrier fluid from the first reservoir and through the feed chamber. Examples of fluids having applications as the first carrier fluid herein include water, water with salt or other additives, organic solvents, or a gas such as nitrogen, carbon dioxide, argon, neon, or a combination thereof.
The present invention further extends to an apparatus for separating and analyzing at least one component of a fluid sample, as set forth above, wherein the means of injecting the pulse of fluid sample into the flow the first carrier fluid comprises a multi-port valve upstream from the feed chamber and downstream from the first reservoir. The multi-port valve is in fluid communication with the first reservoir and the feed chamber, and comprises a port through which the pulse of fluid sample is injected into the flow of the carrier fluid. Optionally, the pulse of fluid sample can originate from a reservoir containing the fluid sample, which is in fluid communication with the multi-port valve. Alternatively, a pulse of fluid sample having a specific volume can be injected into the multi-port valve with a syringe. In a particular embodiment of the invention, the first carrier fluid is a liquid, and the substantially inert purge fluid comprises a gas. Examples of organics which can be separated from a fluid sample and measured with the apparatus of the invention include benzene, toluene, xylene, perchloroethylene, and trichloroethylene, to name only a few.
Moreover, as explained above, an apparatus of the invention comprises a means for flowing a substantially inert purge fluid into the feed chamber after the pulse of fluid sample has passed through the feed chamber. In a particular embodiment of the invention, wherein a multi-port valve is downstream from the first reservoir and upstream from the feed chamber, the means for flowing the substantially inert purge fluid into the feed chamber after the pulse of fluid sample has passed through the feed chamber comprises a second reservoir for holding the substantially inert purge fluid, which is in fluid communication with the switching valve, and a means for operating the switching valve. The switching valve is located downstream from the first reservoir and upstream from the exit chamber, and in fluid communication with the first reservoir and the exit chamber. When switching valve is operated, the first carrier fluid is prevented from entering the feed chamber after the pulse of fluid sample has passed through the feed chamber, and the substantially inert purge fluid is permitted to flow from the second reservoir into the feed chamber. Hence, a flow of the substantially inert purge fluid is formed which flows into the feed chamber, and may substitute for the flow of the first carrier fluid entering the feed chamber after the pulse of fluid sample has passed through the feed chamber. Numerous means for operating the switching valve in the manner described above are readily apparent to the skilled artisan. A particular means comprises a microprocessor which is in communication with the valve. Alternatively, the switching valve can be operated manually. Examples of a substantially inert purge fluid having applications herein include, but are not limited to, nitrogen, carbon dioxide, neon, or helium.
Also, numerous means for creating a flow of the second carrier fluid as described above are readily available to the skilled artisan, and have applications herein. A particular example comprises a third reservoir for holding the second carrier fluid under pressure, wherein the third reservoir is in fluid communication with the exit chamber, and a valve is located downstream from the third reservoir and upstream of the exit chamber. When the valve is opened, the pressure causes the second carrier fluid to flow from the third reservoir, through the exit chamber, the trap means, and ultimately to the detector, which in turn flows the at least one component which passes through the at least one membrane to the trap means and ultimately to the detector. However, when the valve is closed, the flow of the second carrier fluid as described above is not formed. Examples of fluids having applications as the second carrier fluid include nitrogen, hydrogen, or helium.
Moreover, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample as described above, wherein the fluid sample comprises an aqueous solution, the at least one component comprises an organic. Furthermore, in a particular embodiment of the invention, the first carrier fluid is a liquid, and the substantially inert purge fluid comprises a gas. Examples of organics which can be separated from a fluid sample and measured with the apparatus of the invention include nonvolatile organic compounds, and volatile organic compounds, such as benzene, toluene, xylene, perchloroethylene, and trichloroethylene, to name only a few.
Naturally, the membrane of the apparatus of the invention can comprise a symmetrical or asymmetrical structure. In a particular embodiment, the at least one membrane is at least one hollow fiber having a bore and an outer surface, and the at least one fiber is contained within a shell, such that the bore of the at least one hollow fiber membrane defines the feed chamber, and the shell and the outer surface of the hollow fiber define the exit chamber. Furthermore, in a particular embodiment of the apparatus of the invention, a plurality of hollow fiber membranes are enclosed in the shell, forming a membrane module.
Moreover, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample, as set forth above, wherein the membrane comprises nonporous hydrophobic material. Numerous nonporous hydrophobic materials have applications as the membrane of the apparatus of the invention. Examples of such materials include, but certainly are not limited to polydimethylsiloxane (silicone rubber), nitrile rubber, neoprene rubber, silicone-polycarbonate copolymers, fluoroelastomers, polyurethane, polyvinylchloride, polybutadiene, polyolefin elastomers, polyesters, or polyethers. In a particular embodiment of the invention in which the at least one membrane is a hollow fiber, the at least one membrane is comprised of polydimethylsiloxane, has an inner diameter (I.D.) of 0.305 mm, and an outer diameter (O.D.) of 0.635 mm.
Also, the at least one membrane of the invention can also be a membrane composite comprising a porous membrane having a first and second surface, and a nonporous hydrophobic membrane permanently disposed on the second surface of the porous membrane, such that the first surface of the porous membrane is in fluid registry with the feed chamber, and the nonporous hydrophobic membrane is in fluid registry with the exit chamber. Naturally, numerous materials can be used to form the porous membrane of the membrane composite. Examples of such materials include polypropylene, polyethylene, polytrimethylpentene, polytetrafluoroethylene, polyvinylidene difluoride, or polysulfone, to name only a few. In a particular embodiment of the invention wherein the membrane comprises a membrane composite as described above, the pores of the porous membrane range in size from about 6 to about 500 xc3x85.
In addition, the present invention extends to an apparatus for separating and analyzing at least one component of a fluid sample, as described above, wherein the trap means comprises a column having a first end in fluid communication with the exit chamber, and a second end in fluid communication with the detector. The column is packed with a packing material to which the at least one component can reversibly adsorb, i.e. adsorb to and then subsequently desorb there from. In general, any polymeric or carbon based adsorbent may be used. Examples of such materials include, but are not limited to, xe2x80x9cTENAXxe2x80x9d, silica gel, or a carbon based sorbent such as charcoal, xe2x80x9cCARBOTRAP Cxe2x80x9d (Supelco, Inc.), or xe2x80x9cCARBOSIEVExe2x80x9d. In a particular embodiment, wherein the at least one component comprises an organic, the column is packed with xe2x80x9cCARBOTRAP Cxe2x80x9d produced by Supelco, Inc. Furthermore, a sorbent having applications in the invention can be comprised of a combination of presently known sorbents.
Moreover, the column of the trap means can be comprised of a material which does not react with the packing material, the at least one component, and the second carrier fluid. Particular examples of materials which can be used to produce column include stainless steel, xe2x80x9cTEFLONxe2x80x9d, polypropylene, or glass, to name only a few. In a particular embodiment of the invention, the trap means comprises a column made of stainless steel, with a length of 15 cm, an outer diameter of 0.53 mm, and is packed with xe2x80x9cCARBOTRAP Cxe2x80x9d (Supelco, Inc.).
Furthermore, numerous releasing means for releasing the at least one component from the trap means are available to the skilled artisan and have applications in the present invention. In a particular example, the releasing means comprises a means for heating the packing material in the column after the at least one component has reversibly adsorbed to the packing material. As a result of heating, the at least one component desorbs from the packing material, and is flowed to the detector for measurement and analysis via the second carrier fluid. Numerous means for heating the packing material are available to the skilled artisan. In a particular embodiment of the invention, wherein the at least one component is an organic which has reversibly adsorbed to the packing material, the heating means comprises a power supply electrically connected to the column, so that an electric current can be conducted through the column. As a result of this current, the column undergoes resistive heating, which in turn heats the packing material in the column. The organics then desorb from the packing material and are flowed into the detector via the second carrier fluid. Other heating means having applications herein include bombarding the column with electromagnetic radiation, and placing a flame adjacent to the column, such that the column heats up. Furthermore, another desorption means having applications herein is a solvent which is contacted with the trap means, such that the solvent elutes the trapped component from the trap means.
Likewise, numerous detectors have applications in an apparatus of the invention. Examples of applicable detectors include a gas chromatograph, a high performance liquid chromatograph, a gas chromatograph coupled to a mass spectrometer, a capillary electrophoresis instrument, a mass spectrometer, a total organic carbon analyzer (TOC) or an IR, UV, Raman or fluorescence spectrometers, to name only a few.
The present invention further extends to a process for separating and analyzing at least one component of a fluid sample. In a particular embodiment, the process of the invention is practiced with an apparatus comprising a feed chamber having an entrance and an exit, a first flow means for flowing a first carrier fluid through the feed chamber, means for injecting a pulse of fluid sample into the flow first carrier fluid such that the pulse of fluid sample enters the feed chamber, an exit chamber downstream from the feed chamber, at least one membrane through which the at least one component can selectively permeate there through, wherein the at least one membrane is located between the feed chamber and the exit chamber, and is fluid registry with the feed chamber and the exit second chamber, means for flowing a substantially inert purge fluid into the feed chamber after the pulse of fluid sample has passed through the feed chamber, a trap means located downstream from the exit chamber and in fluid communication therewith, wherein the at least one component that permeates through the at least one membrane can be trapped, a releasing means connected to the trap means, wherein the releasing means can release the at least one component trapped in the trap means, a detector in fluid communication with the trap means, wherein the detector detects the at least component released from the trap means, and a second flow means for flowing the at least one component which permeates through the at least one membrane and enters the exit chamber, from the exit chamber to the trap means, and then upon release from the trap means, to the detector. The process of the invention comprises the steps of:
a) flowing the first carrier fluid through the feed chamber;
b) injecting the pulse of fluid sample into the first carrier so that the fluid sample enters the feed chamber;
c) flowing a substantially inert purge fluid into the feed chamber after the fluid sample has passed through the feed chamber;
d) trapping the at least one component which permeates through the membrane to the exit chamber;
e) releasing the trapped at least one component; and
f) detecting the at least one component.
Hence, with the process of the invention, a pulse of fluid sample having a discreet volume ranging from about 1 xcexcl to and including 10 ml can be analyzed.
Naturally, in the process of the invention, the at least one membrane can be symmetrical or asymmetrical in structure. In a particular embodiment, the at least one membrane of the process comprises at least one hollow fiber having a bore and an outer surface, and the at least one fiber is contained within a shell, such that the bore defines the feed chamber, and the shell and the outer surface of the at least one hollow fiber define the exit chamber. Furthermore, also encompassed by the present invention is a fiber module comprising a plurality of hollow fiber membranes surrounded by the shell. In a particular embodiment of the invention, the at least one hollow fiber membrane comprises an inner diameter of 0.305 mm, and an outer diameter of 0.635 mm.
Furthermore, in an embodiment of the invention, a membrane module is used which comprises a plurality of membranes housed within the shell. Hence, the surface area of the at least one membrane can be increased, which increases the efficiency of the present invention.
Furthermore, as explained above, the membrane is comprised of a material through which the at least one component can selectively permeate. In a particular embodiment, wherein the fluid sample comprises an aqueous solution, and the at least one component comprises an organic, the membrane of the invention comprises a nonporous hydrophobic material. Examples of nonporous hydrophobic materials having applications as membranes herein include polydimethylsiloxane (silicone rubber), nitrile rubber, neoprene rubber, silicone-polycarbonate copolymers, fluoroelastomers, polyurethane, polyvinylchloride, polybutadiene, polyolefin elastomers, polyesters, or polyethers, to name only a few. In a preferred embodiment, the at least one membrane of the process of the invention comprises polydimethylsiloxane (silicone rubber).
Moreover, the membrane of the process of the invention can also be a membrane composite, which comprises a porous membrane having a first and second surface, and a nonporous hydrophobic membrane permanently disposed on the second surface of the porous membrane, such that the first surface of the porous membrane is in fluid registry with the feed chamber, and the nonporous hydrophobic membrane is in fluid registry with the exit chamber. Numerous materials can be used in a porous membrane of a membrane composite having applications herein. Examples of such materials include, but are not limited to, polypropylene, polyethylene, polytrimethylpentene, polytetrafluoroethylene, polyvinylidene difluoride, or polysulfone. Furthermore, the size of the pores of the porous membrane can vary, depending upon the types and sizes of organics to be removed from a fluid sample and analyzed. In particular, the size of the pores can range from about 6 to about 500 xc3x85. Naturally, the nonporous hydrophobic membrane of the membrane composite can comprise polydimethylsiloxane (silicone rubber), nitrile rubber, neoprene rubber, silicone-polycarbonate copolymers, fluoroelastomers, polyurethane, polyvinylchloride, polybutadiene, polyolefin elastomers, polyesters, or polyethers. In a particular embodiment, a membrane composite of the invention comprises a polypropylene membrane having first and second surfaces and a layer of polydimethylsiloxane permanently disposed on the second surface of the polypropylene membrane.
Also, numerous means for creating a flow of the first carrier fluid through the feed chamber are available to the skilled artisan and have applications herein. For example, one such means comprises providing a first reservoir for holding the first carrier fluid, wherein the first reservoir is in fluid communication with the feed chamber, and a pump which is in fluid communication with the first reservoir. The pump, such as a peristaltic pump, a gear pump, or a mechanical pump, can be used to pump the first carrier fluid from the first reservoir and ultimately through the feed chamber. Another method would be to place the first carrier fluid under pressure in the first reservoir, and a valve upstream from the feed chamber and downstream from the first reservoir. When the valve is opened, the pressure of the first carrier fluid in the first reservoir would cause the first carrier fluid to flow from the first reservoir and ultimately through the feed chamber. Still another means involves providing a vacuum means downstream of the exit of the feed chamber and in fluid communication therewith. The vacuum means would draw the first carrier fluid from the first reservoir and through the feed chamber, thus creating a flow of the first carrier fluid.
In addition, the step of the process of the invention which involve injecting the pulse of fluid sample into feed chamber, can be accomplished by numerous means are readily available and understood by the skilled artisan. In a particular example, the step involves providing a multi-port valve located downstream the first reservoir and upstream from the feed chamber, and in fluid communication therewith. The multi-port valve comprises a first port for injecting the pulse of fluid sample into the flow of the first carrier fluid. As a result, the pulse of fluid sample is injected into the flow of the first carrier fluid and carried into the feed chamber. Examples of a first carrier fluid of the invention include, but are not limited to water, water with salt or other additives, an organic solvent, a gas such as nitrogen, carbon dioxide, argon, or neon, or a mixture of gas and liquid.
Moreover, in a particular embodiment of the invention, the step of flowing the substantially inert purge fluid into the feed chamber after the pulse of fluid sample enters the feed chamber comprises providing a switching valve which is upstream of the first reservoir and downstream from the multi-port valve, and is in fluid communication with the multi-port valve and the first reservoir. This step also comprises providing a second reservoir for holding the purge fluid, wherein the second reservoir is in fluid communication with the switching valve, and a means for operating the switching valve such that the first carrier fluid is prevented from entering the feed chamber after the after the pulse of fluid sample has passed through the feed chamber, and the substantially inert purge gas is permitted to flow from the second reservoir into the feed chamber. In the feed chamber, the purge gas disrupts the boundary layer which develops on the membrane, and purges any organics remaining in the membrane. Numerous means for operating the switching valve, such as a microprocessor in communication with the switching valve, or operating the valve manually, are readily available to the skilled artisan. Furthermore, examples of substantially inert purge fluids which have applications herein include nitrogen, carbon dioxide, helium, or neon, to name only a few.
In addition, the present invention extends to a process for separating and analyzing at least one component of a fluid sample as described above, wherein the second flow means comprises a third reservoir which holds the second carrier fluid, wherein the third reservoir is in fluid communication with the exit chamber. In a particular embodiment, the second carrier fluid is held under pressure in the third reservoir, and a valve is located downstream from the third reservoir and upstream from the exit chamber, such that the valve is in fluid communication with the third reservoir and the exit chamber. When the valve is opened, the pressure of the second carrier fluid causes the second carrier fluid to flow from the third reservoir, through the exit chamber, through the trap means, and ultimately to the detector. Thus, any component which passes through the membrane and enters the exit chamber will be carried to the trap means, and ultimately to the detector. Another means for creating a flow of the second carrier fluid as described above include a pump, such as a peristaltic pump, downstream from the third reservoir and upstream of the exit chamber, so that the second carrier fluid is pumped from the third reservoir, and a flow of the second carrier fluid through the exit chamber, trap means, and to the detector is created. Still another means for creating the flow of the second carrier fluid involves providing a vacuum pump downstream of the detector, such that the vacuum draws the second carrier fluid from the third reservoir, through the exit chamber, the trap means, and to the detector. Examples of the second carrier fluid having applications herein include, nitrogen, hydrogen or helium, to name only a few. In some instances, organic solvents such as hexane, methanol or acetonitrile may also be used.
Furthermore, the present invention extends to a process for separating and analyzing at least one component in a fluid sample as described above, wherein the trap means comprises a column having a first end in fluid communication with the exit chamber, and a second end in fluid communication with the detector. The column of the trap means is packed with a packing material to which the at least one component can reversibly adsorb. In a particular embodiment, wherein the fluid sample comprises an aqueous solution and the at least one component is an organic, the column is made of a material that does not react with the packing material or the organic, e.g., stainless steel, Teflon, polypropylene, or glass to name only a few. Furthermore, numerous packing materials can be used to reversibly adsorb organics. Examples of such materials include, but certainly are not limited to xe2x80x9cTENAXxe2x80x9d, silica gel, or a carbon based sorbent such as charcoal, xe2x80x9cCARBOTRAP Cxe2x80x9d (Supelco, Inc. Supelco, Pa.), xe2x80x9cCARBOSIEVExe2x80x9d , or xe2x80x9cCARBOPACKxe2x80x9d. Further, the packing material of the column can be comprised of a combination of these sorbent materials. Still other sorbents can be bonded phases such as C18, C8, etc., which need to be desorbed by an organic solvent. In a particular embodiment of the invention, the column is comprised of stainless steel, has a length of 15 cm and an outer diameter of 0.53 mm, and packing material comprises xe2x80x9cCARBOTRAP Cxe2x80x9d.
In addition, the present invention extends to a process for separating and analyzing at least one component of a fluid sample, as described above, wherein the step of releasing the at least one component from the trap means comprises providing means for heating the packing material such that the at least one component, e.g., an organic, can desorb from the packing material, and then be flowed to the detector for analysis via the flow of the second carrier fluid. Numerous means of releasing trapped component from the trap means are available and readily apparent to the skilled artisan. In a particular example, where the at least one component is an organic, the packing material can be heated. As a result of such heating, a component of the fluid sample, such as an organic can readily desorb from the packing material. A wide variety of means for heating the packing material are available to one of ordinary skill in the art and have applications herein. Particular means of heating the packing material include a power supply electrically connected to the column. If the column conducts an electric current, a current conducted through the column will cause the column to heat, which in turn heats the packing material. Other means of heating the packing material include bombarding the column with electromagnetic radiation, or placing a flame adjacent to the column. Alternatively, a solvent can be used to desorb the component from the packing material. In such an embodiment, the solvent is permitted to contact the packing material, such as flowing the solvent through the column. Examples of such solvents include, but are not limited to methanol, ethanol, hexane, toluene, aliphatic hydrocarbons, alcohols, aromatic solvents, methylene chloride, aqueous buffers, or other solvents used in normal and reverse phase elution. The solvent desorption is particularly applicable in the separation and analysis of non-volatile compounds that can not be removed by heating.
Furthermore, numerous detectors have applications in the process of the invention, including a gas chromatograph, a high performance liquid chromatograph, a gas chromatograph coupled to a mass spectrometer, a capillary electrophoresis instrument, a mass spectrometer, a total organic carbon analyzer, or an infra red (IR), ultraviolet (UV), Raman or fluorescence spectrometer, to name only a few.
Accordingly, a principal object of the invention is to provide an apparatus and process for separating and analyzing at least one component of a fluid sample, wherein the pulse of fluid sample comprises a discreet volume, and it is not necessary to flow the fluid sample through the feed chamber continuously.
Another object of the invention is to provide an apparatus and process for separating and analyzing at least one component of a fluid sample, and using a membrane extraction, which is not dependent upon forming an equilibrium across the membrane. As a result, response time for obtaining accurate measurements of the quantity of component in the fluid sample is decreased relative to the response time needed to obtain accurate measurements in a membrane extraction instrument which is dependent upon an equilibrium across the membrane.
Yet another object of the present invention is to disrupt the boundary layer that develops upon the membrane in the feed chamber. As a result of this disruption, the component in the fluid sample is spared the heretofore necessity of diffusing across the boundary layer, and can diffuse directly into and through the membrane. Hence, the lag time between injecting the pulse of fluid sample into the apparatus and detection of the at least one component in the fluid sample is dramatically decreased relative to heretofore known membrane extraction techniques.
Yet still another object of the invention is enable the analysis of fluid samples having a discreet volume